The present invention broadly relates to a new and improved construction of a headbox device for a papermaking machine.
Generally speaking, the present invention relates to a new and improved headbox device for a papermaking machine and comprises a distribution box or distributor and a guide device operatively connected thereto for deflecting and guiding a fiber stock suspension in the direction of the papermaking machine and for distributing the fiber stock suspension across the width of such papermaking machine. The guide device is in flow communication with a nozzle chamber. This nozzle chamber comprises two boundary walls or lip members and a slice opening leading or opening into the papermaking machine and therefore towards the paper web formed thereby. At least one of the lip members or boundary walls or lips of the nozzle chamber comprises at least two sections or zones having different angles of inclination or convergence angles relative to the direction of flow of the fiber stock suspension in the nozzle chamber.
Headbox devices of the aforementioned type are known, for example, from the German Pat. Publication No. 3,321,406, published Dec. 13, 1984, and the U.S. Pat. No. 3,738,910, granted Jun. 12, 1973. According to these patents the guide device is formed, for example, as a perforated plate or as a step-diffusor. This produces a certain turbulence in the fiber stock suspension entering the nozzle chamber from the distribution box in the forward or operating direction of the papermaking machine. The lip members bounding the nozzle chamber are, as a rule, formed as flat or slightly bent or curved walls. Often an adjustable slice shutter or baffle is provided at an end of the nozzle chamber at the slice opening. This slice shutter or baffle is used for effecting transverse profile corrections as well as for increasing stock turbulence. The slice shutter or baffle is inclined with respect to the vertical in the direction of flow usually by an angle of less than 35.degree. and only projects a short distance into the nozzle chamber. This projection of the slice shutter or baffle is, for example, less than 5 mm so that the ratio of the shutter advance to the slice opening width is normally less than 0.5.
These known headboxes exhibit the following disadvantages: frequently insufficient formation quality of the formed paper web; too great a degree of sensitivity of the weight distribution within the paper web in cross-section, with dimensional anomalies or local changes in the width of the slice opening; too great a sensitivity with respect to differences in jet speeds of the fiber stock suspension during transverse profile corrections; as well as in some cases failure to achieve the desired high values of longitudinal/transverse strength of the formed paper web.